Daniel and Kelly’s Extraordinary Universe - How does relativity affect our perception of time?

Episode Date: December 26, 2019

Find out how relativity affects our perception of time with Daniel and Jorge Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

This is an I-Heart podcast. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System

On the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Why are TSA rules so confusing? You got a hood of you. I'll take it off. I'm Manny. I'm Noah. This is Devin. And we're best friends and journalists with a new podcast called No Such Thing, where we get to the bottom of questions like that.

Why are you screaming at me? I can't expect what to do. Now, if the rule was the same, Same. Go off on me. I deserve it. You know, lock him up. Listen to No Such Thing on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. No such thing. I'm Dr. Joy Hardin Bradford, host of the Therapy for Black Girls podcast.

I know how overwhelming it can feel if flying makes you anxious. In session 418 of the Therapy for Black Girls podcast, Dr. Angela Neal-Barnett and I discuss flight anxiety. What is not a norm is to a lot. allow it to prevent you from doing the things that you want to do, the things that you were meant to do. Listen to therapy for black girls on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. Hey, Daniel, what's the most mind-blowing thing that physics has taught us about the universe?

Wow, it is hard to pick just one. Do a top five maybe? No, I want your single, all-time one thing that you think is the most bonkers that we've learned about the universe. Ooh, it's a challenge. All right, I got one. There is one thing about the universe that to me is the most brain scrambling thing I've ever learned.

The hardest thing for me to get my brain around is that people can disagree about the order in which events happened. We don't all see the same things happening sometimes. in the universe? Yeah, you can see things happening in one order, and then I can see things happening in a totally different order, and we can both be correct. Hi, I'm Jorge, a cartoonist, and the creator of PhD,

comics. Hi, I'm Daniel. I'm a particle physicist sometimes and a podcast host other times and everybody disagrees about when I do what. So welcome to our podcast. Daniel and Jorge agree to disagree about the universe. In which we explain to you the craziest, the most amazing but true things about our universe. Yeah, and this is again a production of iHeart Radio. And in our podcast, we try to take you to the forefront of science to talk about the craziest things that. scientists are thinking about today and also delve into the history of science to tell you why we think the universe is so nuts and how we figure that out. Is there a history of science, Daniel, or is that also open for disagreement? People disagree about in what order we discover things or what was the

most important or how we changed people's minds. Yeah, I think in our podcast, we also not just talk about scientific discoveries or scientific theories, but also a little bit about how that affects how we see the universe, you know, and how it challenges what we believe about how the universe works. Yeah, absolutely. I think a lot of the deepest questions in physics come from a sort of a philosophical motivation. We want to know how the universe works

because it matters to us that we can make sense of the universe. And when we ask the universe questions and it gives us answers that force us to totally change the way we think about the universe, that has pretty deep philosophical implications. And so that's sometimes the most fun topic. Yeah. And so basically we're just trying to blow your mind

in the gentlest, most podcast-friendly way possible. Or we're trying to share with you how the minds of physicists have been blown. And we want your mind to be blown just as much. But yeah, a little bit more gently. Yes, please. I'm not sure my brain can handle this much mind-blowingness in one hour.

But you know, when I was learning physics as a undergrad, I remember these moments when I finally really deeply understood a concept and that concept would force me to relax or destroy or get rid of some assumption I had about the universe. And I realized that that just wasn't true, that the way I'd been thinking about the world was just fundamentally wrong. Yeah, it's amazing. And so today we'll be talking about one such topic that honestly gives me a headache every time we talk about it, Daniel. We've written about it in actually a couple of chapters in our book.

We have no idea, a guide to the unknown universe. And I have to admit, I never really got my head around it. I authored the book, but didn't actually 100% understood what was in it. Yeah, and this is a topic that people email us about. They ask us about. They listen to some of our podcasts about it and still write in with questions. I think there's a lot of popular misconceptions about how this works. And some consequences that I think a lot of people have not really realized.

There's some really deep philosophical implications to these ideas that I don't think have been widely enough appreciated. Yeah, so to the end of the podcast, we'll be talking about How does relativity affect our understanding of time? Time, time, time. Or I guess the short title is,

is there a consistent order of events in the universe? Yeah. And spoiler alert, the answer might be no. It's relatively surprising that the answer is not what you expect. We've talked on this podcast before about time dilation, the effect of speed on the rate of which clocks move forward. And that's weird and that's hard for people to get their mind around and there's some misconceptions there.

But, you know, time and relativity is even weirder than that. It's more than just making things run slowly or making things run quickly. It's about how things happen here versus how things happen there. Do you think age also affects how you perceive time? I feel like my kids have no patients at all, and the world just moves at a snail's pace for them. Whereas for me, as I get older, things just move faster. Well, I mean, I move slower, but the world seems to move faster.

Yeah, and I think that actually you raise an interesting point because we are all imperfect observers. If you just sort of watch something and describe it later, there's all these studies about how people give terrible accounts, you know, even eyewitnesses give different accounts of the same, events. And so that's certainly one problem. It's like people are unreliable observers. But even in the case when everybody was a perfect observer, everybody had a video camera, everybody had, you know, perfect measuring devices and everybody accounted for transmission of light and all that stuff. Even in those cases, it's hard to make sense of the universe. Like if we were all robots with the exact same, you know, clock in our chips and we were all measuring things exactly. It would still be kind of a weird universe where not. Not everyone would agree, maybe, on the order of events.

Yeah, precisely. And you have to separate those because we're interested, not in the question of, are people good eyewitnesses? Because we already know the answer to that is no. But the question of how does the universe actually work? Because we want to know the answer to the question not just for humanity, but in general, you know, deep fundamental question. So that when the aliens come and we talk to them about physics, we can make sense of what they've learned. And we don't want to learn human physics. We want to learn fundamental physics.

And so this idea of time dilation, this idea that time moves slowly, depending on maybe how fast you're going or where you are, is kind of weird and pretty mind-blowing. And so we were wondering out there how many people really sort of understood what it means and what the ramifications, what it means for our basic understanding of time. So I walked around campus at UC Irvine and I asked folks, not people in the physics department, Not people who've taken my class on special relativity. Just random people on campus willing to answer questions from a scruffy-looking physicist. So think for a moment. What do you know about how relativity affects our understanding of time? Here's what people had to say.

Do you know how relativity affects our understanding of time? No, I do not, actually. No, I'm not sure. Newton's theory of relativity? Einstein's theory. Oh, Einstein's? I'm sorry. Is this a physics, like a physics question? I don't know much about physics.

I don't know how to answer that. No, I'm an English major. Okay. I feel there was a whole, like, demonstration of that where if, like, you go at, like, in a spaceship, like, near the speed of light or something, and then you can come back and then, like, some, like, amount of time has changed on Earth

while, like, no really time has changed for you or something like that. Yeah, I'm thinking planted of the apes when they're in the spaceship, and then by the time they come back, they've only aged a couple years, but time on Earth has passed a lot, because they're traveling at a different speed relative. Planned the Apes is a well-known physics documentary, right? Yes, yes.

Classic. I believe relativity, that's from Einstein, and it's the idea that, like, time doesn't flow at the same rate, like across the universe. I think something, like, I think gravity or something affects, like, how it flows in other places. All right, a couple of knows, but a couple of people did have a lot of pretty good ideas,

or at least they set a lot of physics-y-term. You mean like Newton's theory of relativity? Like the Planet of the Apes? You know, I've seen that movie. Yeah, Planet of the Apes. That's a documentary by physics. Yeah, there you go. Now, you're right.

People had, the people who knew anything about it definitely knew that relativity and time are connected and that relativity changes how time moves. And I think already that's a big success, right? The idea that time is not universal, that we don't have clocks everywhere in the universe, ticking forward at the same rate. That's a big step forward to

to break that assumption. You don't think you didn't have a theory of relativity? I mean, he could have had one about his relatives or something, but he's not the one that caught on. Right. His theory of relativity was, don't bring up politics at Christmas dinner.

Yeah. Also useful things to live by. But yeah, I think it seems like maybe there is a general sense, right, that relativity affects. our understanding of time and makes things weird, but maybe a lot of people don't know how or

why. Yeah, and I think also there's a lot of misunderstandings, based on the emails that we get from listeners who are asking us questions about relativity and tweets and stuff that people have posted, I have the feeling that people think that if you move fast, then your clock will slow down,

which is not the right way to think about time and relativity. That's how I thought time and relativity worked, so we're in for a long conversation. so people have been writing with questions about time yeah a lot of people ask the questions like what is it like to be a photon or how does a photon move at the speed of light if moving at the speed of light means that its time is frozen

they're asking what would be the human experience of moving at these velocities where physics gets really weird yeah and so let's clear that up first of all the key thing to understand about relativity and time and clocks is that the speed at which a clock moves depends on its relative velocity to you. Now, these things are always relative. So if you're holding a clock and it's not moving relative to you, it's just going to go forward at one second per second. Like you always experience time the same way

because you're not moving relative to yourself, right? It's only relative motion that distorts time. If you see a clock moving fast and you're watching the face on that clock, then it runs slowly, but only according to you. I think maybe we need to step back a little bit. Paint the picture of like, I'm standing here and I'm holding a clock in front of me.

You're saying that because the clock is not moving relative to me, I'm not going to see or feel anything strange about that. That's right. Like it's going to, I'm going to hear it ticking and it's going to sound like it's ticking at one second percent. That's right. And you always experience time the same way. Like you don't experience time going,

slowly or going quickly. But if I'm zipping past you at half the speed of light and I look at your clock, then it looks to me like your clock is running slowly. Now, according to you, the clock is not moving. You're holding it. So the clock runs at the normal pace one second per second like usual. You don't experience time slowing down just because I'm moving past you and I see your time slowing down. But again, if I'm zipping past you at half the speed of light, then it looks to me like your clock is running slowly. Well, first of all, how would you look at my clock? If you were moving back back.

Would you have time, Daniel, really? I'm super robot observer. Remember, I can observe anything accurately. Oh, I see. You're running at a bazillion gigahertz. I am super physics grad student. No, you have to imagine I have like some awesome telescope and I'm watching the face of your clock or something. All right. So I'm in my little space here and I have my clock and it's taking away. And you're zooming by. And as you're zooming by, we're, we're, we're, we're, we're going to go into super matrix slow motion here.

And so you're looking at my clock and my clock is moving relative to you like you're seeing it go by. And if you were to measure its ticks, to you, it would seem like it's ticking slower. Like tick, tick, right? Is that kind of what you mean by that my clock seems slower to you?

Precisely. And your clock seems slow to me but it doesn't seem slow to you. It looks to me like you are aging slowly because your time is running slowly. In a year for me, less time will have passed for you and I will see you aging slowly. But for you, time just moves forward because, again, you're not moving relative to you. The thing to remember is moving clocks run slowly. So you're not moving relative to yourself, so your clock doesn't run anymore slowly. But they only move slowly relative to the person who's not moving.

Yeah. Everybody has a frame of reference that's centered at them, and things are moving or not moving in their frame. And if they're moving fast, then their clocks run slowly. If they're not moving, then their clocks run normally. All right. And that's basic general relativity, is that time seems to slow down in a pocket of space that's moving fast relative to you. So that's special relativity. General relativity has to do with how space is bent by mass.

special relativity, all these effects of light speed and clocks and stuff. And it's not just that it appears to go slowly. Like, your time really does move slowly, according to me. And that's the crux, is that I have a story about the universe that I'm telling based on my perfect observations, and that's a true story. And you're telling a different story about the order in which things happened and the rate at which time flowed, and that's your story. And your story is different because you're in a different place

at a moving at a different speed relative to me. But both of our stories can be correct. Meaning, I can experience my clock taking it one second per second, but you would say that my clock is not taking it one second per second. Precisely. And it's not just that it appears that way. It actually is. I guess it depends on what the definition of is.

Thank you, Bill Clinton. And so, you know, a lot of people write in, they say things like, you know, a photon is moving at the speed of light, which is true. And if a photon had a clock on it, somehow, I don't know how you could have a photon with a clock on it, but imagine you could, then wouldn't that clock be frozen?

Yes, true, because something moving at the speed of light, its time slows down to an effective rate of zero. But that doesn't mean that photon is not experiencing time. It's experiencing time maybe normally, but by the time it blinks, it's made it across the whole length of the universe. Yeah, because from the point of view, the photon, I guess, The whole universe is moving past it at the speed of light.

And so the whole universe is like length contracted down to zero. We'll have to do a whole other episode about the effect of relativity on length and distances and crazy stuff like that. But the idea is that moving clocks run slowly. That's the thing to keep in mind because all these statements have to be made in a relative sense. You can't say, I'm moving really fast and therefore my clock has run slowly. You have to say, I'm moving really fast relative to what? and it's for that observer that your clock is running slowly, not for you. Right, because I'm sitting here in my pocket of space and I'm watching use it by.

And if I look at your clock, I would say that your clock is moving slowly. And you would be correct. And I would look at your clock and say, your clock is moving slowly and I would be correct. Well, it would be a really short conversation then if you were moving past. I'll have this beat of like, hey, he's gone already. Forget it. If this podcast was in stereo, we could do some cool effects there, zooming back and forth. Make it happen, engineers.

You started to treat engineers the same way I have now. Engineers are just people out there to make things happen. I think people who make things happen are awesome, by the way. My caveat to that. Yay, engineers. All right, so that's special relativity. That's the general idea that time seems to move slowly. depending on how fast you're going relative to other people who might be watching your clock.

Yeah, I would say time moves slowly for people that are moving fast relative to you. I think that's pretty close to what I'm sure it's not. We can disagree on that. All right, so that's special relativity. And it creates a weird situation for arguments about what happened and in what order things happen and just in general about time. and the universe. So let's get into that.

But first, let's take a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush. Parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the T-Dade. AWA terminal. Apparently, the explosion actually impelled metal glass.

The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even hard. harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't is a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone. Now hold up, isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them.

I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast. on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast. Here's a clip from an upcoming conversation about exploring human potential. I was going to schools to try to teach kids these skills, and I get eye rolling from teachers or I get students who would be like, it's easier to punch someone in the face.

When you think about emotion regulation, like you're not going to choose an adapted strategy, which is more effortful to use, unless you think, there's a good outcome as a result of it, if it's going to be beneficial to you. Because it's easy to say, like, go blank yourself, right? It's easy. It's easy to just drink the extra beer. It's easy to ignore, to suppress, seeing a colleague who's bothering you and just, like, walk the other way. Avoidance is easier.

Ignoring is easier. Denial is easier. Drinking is easier. Yelling, screaming is easy. Complex problem solving, meditating, you know, takes effort. Listen to the psychology podcast on the IHeart Radio. Apple Podcasts or wherever you get your podcasts. All right, Daniel, let's maybe get into the details here

of how time or how special relativity messes with our understanding of time. So what's the, are we going to paint a picture for people? Are we going to be on trains, on rockets, or is Alice and Bob going to be involved? Yeah, let's mix it up a little bit because usually special relativity is like people on trains because when they invented special relativity, trains were like the fastest thing around. But that's a little old. And usually quantum mechanics thought experiments involve two experimenters named Alice and Bob. But let's mix it up.

Let's use Alice and Bob for a special relativity thought experiment. Let's use Alicia and Roberto. Perfecto. Just to mix it up a little, spice it up. All right. So if Alicia and Roberto are having a race, race. Say it's like some family event, right? They're there with their relatives, so it's all about relativity. And they've all had their, you know, Christmas ham or whatever, and now they're

going to go out and make an ill-advised 100-yard dash in the backyard. And they're both really fast. And people are watching the race. And then afterwards, of course, they're going to argue about who won. But let's say that everybody who's watching the race is a perfect observer. Everybody has a clock that they can start and stop, and everybody's really paying attention. and knows what they're doing. Then the question is, who wins the race? So they're both at the starting line. You know, we say go.

They start running towards the finish line. And I'm sitting there at the finish line waiting to see who gets there first. Precisely. And the amazing thing is that there is no one single correct answer for who wins this race. Now, if you're sitting at the finish line and you're...

My money's on Alicia, to be honest. You've always liked her more than Roberto, and frankly, Roberto's pissed about it. Well, she's my cousin, so. So is Roberto, man. What's wrong with you? Anyway, if you are sitting at the finish line, so you have no velocity relative to the ground, then you might see Alice, you might see Alicia beat Roberto in the race. Cool.

And you might think, well, that's it. That's the answer, right? She won time to celebrate. So I'm sitting in a chair by the finish line, and to me, Alicia was running faster than Bob, so she got to the finish line first. Precisely. And you might think, well, that's it, right? Other people might see it from another angle, or other people might be sitting somewhere differently. Or maybe even if somebody is driving by in a car, they might see the velocity of Alicia and Roberto be different.

But everybody should agree about the basic facts because there is a single thing that happened. That's the way you grew up thinking about the universe. that's what sort of makes intuitive sense to you. It's true, right? Like if there's somebody sitting on the opposite side of the finish line, sitting in a chair as well, you're saying that they could also see a different result, even if they're not moving like me.

Actually, the other observer would have to have a different velocity than you, not just be separated in distance. But you're right. The order of events that you see depends on two things, your location relative to Alicia and Roberto, and your speed relative to them. So if you are in a, to make it simple, if you are in a car and your car is super fast and you're going at like half the speed of light or something, then you could see the race differently and you could see you have a different outcome. You could see Roberto cross the finish line before Alicia.

This is not some trick where like the light from you takes longer to get there or anything like that. But if you have a different relative distance to Alicia and Roberto and you're moving at a certain velocity, then you can actually. actually see the events happen in a different order. I am sitting my chair. I'm going to measure who wins. But if you're moving, driving by at really fast velocities, you might see something totally different than what I see. Yeah.

I could see Roberto cross the finish line before Alicia. And I would also be right. But do you have to drive towards them, perpendicular to them? You know what I mean? like what's actually happening there to make you see something different. No, let's imagine it's pretty simple. Let's say I'm moving in the same direction

as Alicia and Roberto. You started way before them or way back, and by the time they cross the finish line, you're crossing the finish line too, but you're going really fast. That's right. I started on the moon or something like that

so that I'm passing the race at exactly the same moment that Alicia and Roberto were actually running so that I'm parallel with them, but moving at some very high velocity, then I can see the order of events differently. I can see the race start, and then I can see Roberto finish the race before Alicia.

Even if you, sitting on your plastic chair, eating leftovers while you're watching, sees Alicia pass the finish line first. Yeah, no, I understand that's what is maybe happening, but I guess I'm trying to just understand maybe for the people listening to this is why. Like, is there any way that we can understand And with this example, like how special relativity makes it so that we see different things?

Well, special relativity tells you that the flow of time is dependent on velocity, right? And also on distance. So the way the clocks work depends on how far away they are and how fast they are moving. So we talked earlier about how the speed that a clock will move depends on how fast it's moving relative to you. That's true. but there's another factor we didn't get into, which is that it also depends on where the clocks are. And so if you see two clocks moving at the same speed relative to you,

but there's a distance between them, then you see a different effect on the two clocks. It's not just dependent on the velocity. It's also dependent on the distance to the clocks. Because fundamentally what's happening is that the universe has sort of like a clock at every location. And the way those clocks, flow depends on your velocity relative to them.

Okay, so now you're talking about like a third person. The key thing is this separation between Roberto and Alicia. If Roberto and Alicia are like literally on top of each other, then you don't get this effect. But if there's a gap between them... That's a different picture there. That doesn't happen at family gatherings. But if there's a gap between them, right,

if they're a meter apart or five meters apart or something. Then their clocks are going to run differently. but how does that affect who I see getting to the finish line first? Like it shouldn't matter to me that their clocks are running slower. How does that affect how I see them and how you would see them? Well, if you see Alicia's clock running more slowly than Roberto's, then she's not going to be running as fast. I only know that their clocks are running slower because they're moving relative to me.

So why? Imagine that there's a clock floating in space next to Alicia and Roberto, right? It's some drone robot clock that hangs out right next to them and it can perfectly synchronize its motion and location relative to them. To which one? One for each of them. Then you would see Alicia's clock running at a different rate than you see Roberto's clock because not only do they have a velocity

relative to you, but there's a distance between them. You have a different location. And so the way at which time flows depends not just on your relative velocity, but also where you are relative to that observer. All right. So you're saying that I'm going to measure. I might measure Alicia or Roberto winning sitting by the finish line, but somebody else, you on your car,

running towards the race at an angle maybe or going at a certain speed, close to the speed of light, you might see something different than what I see. Precisely. If you are sitting there and you have no velocity relative to the ground, maybe you see them tie because they've been training forever and they've been working on this, and they're both really, really fast.

But then if I am zipping past in a car, moving really fast, then I could see Alicia reached the finish line before Bob reaches the finish line. And, you know, it's tricky when you're thinking about special relativity. It's really easy to get yourself confused. But the most, the clearest way to think about it is in terms of events and when those events happen. And so you see Alicia reach the finish line before Roberto. Now, you might think, how is that possible? Like, they're running at the same speed. Well, you know, there's also a question of, did you see them leave the starting point? at the same moment, right?

Because if you're moving at a high speed relative to the race, then time is distorted for you. Your view of their time is distorted. So you're saying it has to do a little bit with the idea that time for Alicia and Roberta are going to be moving differently relative to me and to you. And so that's going to affect kind of who we see crossing the line first. Precisely.

If you are sitting there in a plastic chair finishing your dinner and watching Alicia and Roberto cross the finish line at the same moment and you see their clocks moving at the same speed and you see them also starting the race at the same moment, right? I think maybe that's the key insight. Whereas you maybe saw them start at different times.

Yeah, I see Roberto win, but it might also look to me like Roberto cheated. Like he left the starting point at a different moment, right? This concept of simultaneity of things happening at the same moment depends on your relative speed to those events and your distance from them. So like in the Jorge Olympics, backyard Olympics, Alicia would win,

but in the Daniel moving at the really, in a really fast car Olympics, somebody else, not only would they, somebody else would win, but somebody else would have cheated. Yeah, but, you know,

according to me, they've cheated, but according to you, they haven't. And then we have a third cousin, you know, and she is driving her even faster car, the other direction,

right, than that different belgative velocity, It can cause a different distortion of how time works from her perspective. And she could see Alicia totally blow Roberto away instead of just winning by a little bit. Well, I think at the end of the day, you know, by the time they finish, you're going to be, you know, hundreds of thousands of miles away. And so who cares what do you think? And if you think they cheated is how I would put it, whereas I'm right there with the medals ready to hand them out, you know? Precisely, yeah.

So in the end, your point of view is most important because you're handing out the trophies. But the point is that the folks in the car driving past at high speeds, they see different order of events and they're not wrong. It's not like they messed it up because they're moving fast or it took more time to get to them or any sort of trick like that. If we're assuming perfect robotic observers, they just see the order of events differently because time is moving differently according to them. And their account doesn't have to be wrong. It's just different. Just like the astronaut or just like the photon, it's not like the photon is wrong. It's just that they experience things differently because they're moving at a different speed.

Right. And, you know, we as humans grew up in a world where things move pretty slowly. And so we can, in the end, reconcile usually a single series of events. Like, this happened, then that happened, then this other thing happened. And sometimes it's hard to disentangle people's emotions and their bad eyewitnesses. But, you know, if we had video cameras at everybody's location, usually we can disentangle this stuff. But as you get next to the speed of light,

as you get things moving really quickly, then that breaks down. And time flows differently in such a way that it can actually change this order, which means that people have a different account of what happened first and what happened second. And I remember the moment in my, you know, junior special relativity class

when I learned this, it just blew my mind that there's not like an universally agreed upon order of events for stuff happening. But mostly we would be, We would be, I don't want to say disagreeing, but we would be seeing different things, but that usually sort of happens more prominently when you get closer to the speed of light.

Yeah, you can't notice these effects at slow speeds. Even for the example of Alicia and Roberto, if they're running at fairly low speeds, you know, 10 meters per second, which is actually pretty fast, and they're running only 100 meters, you'd have to be going really fast to change the order of events by even nanoseconds. So these effects are very small unless you're approaching the speed of light.

Yeah. Okay. Yeah. It's not like Roberto can argue that he should have gotten the medal because the likelihood that there's an observer going to near the speed of light near my backyard is maybe not zero, but unlikely. Well, it depends on who's listening to his argument. I might be more sympathetic to it. I might be like, you know, you're right, Roberto. There is some universe in which you did win this and you were jilted from getting the medal.

Yeah, but really you would be like, yeah. Robert, I think you're, uh, and then you'd be gone. That's right. Daniel thinks you won, and he's your medal, but he's now by Alpha Centauri, so you're out of luck. Yeah, so go catch up if you want your medal. Your medal. All right, that's pretty mind-bending, that so many things kept be happening in my backyard, or that I have new cousins called Alicia and Roberto. But let's talk about now whether, you know, how that makes any sense or how physicists are able to wrap their heads around. on these kinds of things.

But first, let's take a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal Apparently, the explosion actually impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene.

In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit.

Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't. trust her. Now he's insisting we get to know each other, but I just want her gone. Now hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio. app Apple Podcasts or wherever you get your podcast. I'm Dr. Scott Barry Kaufman, host of the psychology podcast. Here's a clip from an upcoming conversation about exploring human potential. I was going to schools to try to teach kids these skills and I get eye rolling from teachers or

I get students who would be like, it's easier to punch someone in the face. When you think about emotion regulation, like you're not going to choose an adapted strategy which is more effortful to use unless you think there's a good outcome. a result of it if it's going to be beneficial to you because it's easy to say like like go you go blank yourself right it's easy it's easy to just drink the extra beer it's easy to ignore to suppress seeing a colleague who's bothering you and just like walk the other way avoidance is easier ignoring is easier denial is easier drinking is easier yelling screaming is easy complex problem solving meditating you know takes effort listen to the psychology podcast on the

iHeart radio app apple podcast or wherever you get your podcasts. All right, Daniel, so according to physics, my backyard Olympics are totally arbitrary, meaning that to me the outcome might be one thing, but to you moving at close to the speed of light, the outcome might be different. And you're saying that this really throws into question

this idea of simultaneously in the universe, like things happening at the same time because things happening at the same time might depend on who's measuring whether they happen at the same time. Yeah, and there's a kind of thing that we have to do in physics all the time is we think the universe works a certain way,

and then the universe shows us that, nope, it doesn't. And that momentarily throws us for a loop. We think, what? You know, you can do the same experiment twice and get different outcomes because quantum mechanics is really probabilistic or time doesn't work the same way, for everybody, but we don't give it up.

We don't say the universe, therefore, makes no sense. What we do is we sort of retreat to a looser sense of what sense means. We say, all right, we can't make those assumptions. What assumptions can we make? What can we say about the universe? And we find another way for it to make sense. They sort of don't make sense in the sort of like Newtonian, you know, high school physics, or, you know, what we learned as babies, how the world works.

It doesn't make sense in that way. Just like maybe quantum mechanics doesn't make sense to us, but it does make sense if you sort of expand and you understand the sort of the equations that are happening. Yeah, like in quantum mechanics, you can't say that the universe is deterministic. You can't say that if you do, if you shoot an electron at the same atom in exactly the same way, you'll get the same outcome every time. You won't because there's some randomness there.

But what you can do is you can say that there are still laws of physics, and those laws of physics determine which random outcomes are more likely or less likely. So you've sort of taken a step backwards. You said, well, I can determine a specific outcome, but I can say something about the distribution of outcomes. And you can do something sort of similar for relativity. You can take a step back and you can say, well, I can't say that everybody has to agree about the order in which things happen in the universe.

Okay, what can I say instead? Well, you can say that everybody sees things happening according to the same law. So, you know, you sitting in your plastic chair at the edge of the finish line, you see things happening according to a certain set of laws of physics. Me and my high-speed Lamborghini, I see things happening according to the same laws of physics. Now, I see different things happening, but they're following the same laws. Right. You're basically saying that the laws of the universe account for this difference of point of view in order of events. And so then it makes sense. It's like you're saying the laws of physics don't make sense, and that makes sense.

They make a different sense. They don't make common sense, but they make mathematical sense. They certainly don't make common sense. No, it means that you can use the same laws to predict what's going to happen as I can use in my frame. So no matter how fast you're going and where you are in the universe, you should be able to use the same laws to describe what you see and to predict what's going to happen. And those laws should work. so we can still make that requirement. The events can be different from place to place

and the description of what happened can be different from place to place but each one follows the same set of rules. Right. There's nothing inconsistent about the universe is just that the rules of the universe allow for this kind of different points of view depending on your speed.

Precisely. And your point of your direction. Precisely. And I think it's a tiny bit deeper than that. It's not just that we understand how to translate what you see to what someone else going at high speeds we'll see we do understand that and that's cool but the deeper bit is that the same rules apply no matter how fast you are going so you can use the same laws of physics

now you and i can disagree about the order that we saw the race be run and who won and who cheated but we agree on the rules of physics that describe what we saw not just how it translates from what i saw to what you saw we see them follow the same rules and i think that's pretty deep and then there's one more thing that we can still cling to. We can say that even though things can happen in a different order, sometimes there are some rules about that. You can't arbitrarily reorder the universe. Oh, I see.

Yeah, this is what you were saying earlier. There's a difference between simultity and causality. That's right. They're both impossible to pronounce words. Yeah, and kru, cool, cool. Obviously, if I can reverse the order there of events, I would say causality, correct. Yeah, the key thing is that you can use velocity and distance and all these crazy relativistic effects to reverse the order of some events, events that are not causally connected, events where one didn't cause the other one, but some things you can't.

Meaning we can see different outcomes of a race between Alicia and Roberta, but we probably wouldn't disagree on a relay race with Alicia and Roberta. Yeah, or for example, there's no. speed at which you can go in order to see Alicia finish the race before she starts. And that order of events definitely happens. She starts the race and then later she finishes. Now, when she finishes relative to Roberto, that's a different question. We can zoom around our spaceships to get whatever answer we want. But you'd have to go faster than the speed of light in order to reverse two events that are causally connected where one caused the other one. So that's why you can't, for example, make the big bang happen at the end of the universe or

you know all sorts of other crazy stuff there's some freedom here to move around the order of events but it's not pure total freedom don't go crazy people right meaning it's not that the whole universe is open to interpretation because you know

like the Big Bang happened and earth formed and it's not like moving at any speed will change anything about that but maybe small things like small things like some people might say happened or not happen simultaneously then people moving at different speed

might have a different point of view. Yeah, and the size of these things depends on sort of how far away they are. Like things that are in another galaxy they're really, really far away, nothing over there is causally dependent on anything we do because nothing we do here

can affect it for a long, long time because of the speed of light. So things happening on the other side of the universe, the order in which those events happen is almost irrelevant for us. We could change those. events by a billion years probably because it makes no difference to the causal connections because nothing that happens here affects that for a very long time things that are close together right

it's much more sensitive you can causally affect the things close to you you can touch things over you can shine a flashlight and affect things nearby so you're saying that a raise in a backyard in another galaxy could have happened before or after my race maybe because there's a long separation between them. But because they don't affect each other, then it's okay to sort of move them around in terms of our perception of when they happen. Yeah. And we talk about this thing called the light cone, which is this cone in space that opens up at the speed of light around you. You can only affect things that are in your light cone, things that are sort of downstream from you. You can affect them. Those things are causally dependent on what you do. Things that are not in your

light cone, that they're too far away from you for you to affect them now or in the near future, there's no way for you to have any influence over them. So their relativity can go crazy and it can change the order of events without breaking anything. Right, but we're still all in the same universe, right? We are all in the same universe, yeah. Yeah, it's not like I'm disconnected from that galaxy or to things that are not in my light cone. Something in my light cone might be in that other things, light cone, and so I'm still connected to the rest of the universe. Yeah, and your light cone goes on forever, and so eventually it will encompass the entire universe, right? Things you do now could affect things 15 billion light years away, but it's going to take

15 billion years. So your light cone is growing, and eventually everything's light cone overlaps, right? So things do come into contact. I don't think my ego needs any more feeding, Daniel, to think that I can affect the entire universe eventually. That's a pretty big step up from handing out medals from the backyard Olympics to affecting the entire universe. Small steps, my friend.

Backyard Olympics today. Galaxy collisions tomorrow. No, I think the thing to understand is that we are all living in the same universe and that universe has a certain set of rules, but those rules are not necessarily the rules you thought they were. And it allows for some fudging and some flexibility and for some weird stuff to happen. But it's not throwing everything out the window.

It has to be consistent with the universe we've lived and the things we've observed. You don't get to go really fast and go back in time, You don't get to go really fast and, you know, change your order from a chicken sandwich to a burger or whatever, right? There are still rules to the universe. They're just not as hard and past as you thought. And fundamentally, it means that the universe is different from the one we thought it was. You know, the way quantum mechanics has deep implications for the way the universe works, but it doesn't really change your day to day, right?

If you don't go to work, you still lose your job, right? There are some things that are deterministic. If you don't fix climate change, the planet might get too hot. Right? It's not like we can disagree about that. No. And this is not an excuse to say that you can have just whatever facts you want, right? It's just that the facts are sort of local, right? Depending on where you are and how fast you're going, your account of what happened in the universe is different. But it's always just blown my mind that people can have correct but different accounts of the order in which things happened.

Although I think one thing that never changes is I think Roberto is a cheater. I think he cheats in any universe, in any galaxy, no matter. who you're looking, who's looking at. I think the question in my mind and in listeners minds is, do you actually have a cousin named Roberto? And if so, does he listen to the podcast? Oh my God, I just realized I do have a cousin named Roberto. That's what happens when you have 37 cousins. I don't mean to say you're a cheater.

I'm talking about our other cousin, our third cousin, Roberto Prime. And do you have a cousin named Alicia? Because now she's going to be your favorite cousin. Oh, let me think. I don't have a cousin named Alicia. Let me think. Who has to say, let me think? You have like dozens and dozens of cousins.

Someone who has 36 cousins needs a little bit of a second there to think about. Where were you last night, honey? Hmm, let me think. You know, never a very inspiring answer. Especially in Latin American culture where everyone has a nickname that is totally unrelated to their actual name. You have to think a little bit. Oh, so when you're talking about Roberto, that's actually a nickname for your other cousin, Nicholas or something. Yes, that's right.

Something like that is how it goes. It sounds like a Russian novel. All right. Well, I hope that sufficiently altered or bent your mind there for at least the time of this podcast. And remember that the universe is crazy, the universe is bonkers, but it's our universe, and we love it. And eventually, we hope it will make sense to us. That's right. Just like we love that crazy cousin, we all have.

Who we now have to apologize to after this podcast. That's right. Well, nobody listens to this podcast, I think. All right. Thanks everyone for listening and for asking us crazy questions. And if you still don't understand special relativity and the flow of time, don't worry, nobody else really does either. Thanks for listening. See you next time. If you still have a question after listening to all these explanations, please drop us a line.

We'd love to hear from you. You can find us at Facebook, Twitter, and Instagram at Daniel and Jorge. That's one word. Or email us at Feedback at Daniel and Horhe. Thank you for listening and remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio. For more podcasts from IHeartRadio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then everything changed.

There's been a bombing at the TWA terminal, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Why are TSA rules so confusing? You got a hood of you. I'll take it off. I'm Manny. I'm Noah. This is Devin. And we're best friends and journalists with a new podcast called No Such Thing,

where we get to the bottom of questions like that. Why are you screaming? I can't expect what to do. Now, if the rule was the same, go off on me. I deserve it. You know, lock him up. Listen to No Such Thing on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. No Such Thing.

I'm Dr. Joy Hardin-Bradford, host of the Therapy for Black Girls podcast. I know how overwhelming it can feel if flying makes you anxious. In session 418 of the Therapy for Black Girls podcast, Dr. Angela Nielbornet and I discuss flight anxiety. What is not a norm is to allow it to prevent you from doing the things that you want to do, the things that you were meant to do. Listen to Therapy for Black Girls on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. This is an I-Heart podcast.